As Oregonians dig out from heavy snows along the northern Willamette Valley and coast, they’re wondering how forecasts for a light dusting above 500, turned into more than 10 inches on the valley floor.
Forecasters knew there could be some snow on Wednesday because a low-pressure trough was headed in northwest Oregon’s direction.
But rather than blowing over, the trough stalled just off the north coast, meaning snow conditions stayed in the same place all day and all night.
National Weather Service meteorologist Colby Newman said their models didn’t do a good job of predicting the stall.
“We have a big data vacuum to our west,” Newman said. “There are not many weather stations over the ocean. And we don’t have a good way of getting a lot of weather observations, out over the ocean.”
In addition to that lack of ocean data, Newman said there was a combination of factors at play.
“We have satellites that the models are using to ingest that data and it has made these surprises a lot less frequent than they used to be,” he said. “But there’s definitely room for improvement.”
He said the snow could have ended up as rain if the stall had happened elsewhere.
“If the low set up 30 miles off the coast,” he said, “we probably would not have gotten any snow yesterday.”
So a small shift in the location of where the low-pressure system settles makes a big difference in which area gets hit with snow and whether that snow falls as rain instead.
Without more research, it’s not clear whether Wednesday’s storm is linked to climate change. Every now and then, northwestern Oregon simply gets socked in with snow.
“We do get snowstorms on occasion of this magnitude,” Newman said. “It’s rare, but we do get them.”